Control method for memory cell

ABSTRACT

A control method for at least one memory cell is disclosed. The memory cell includes a transistor and a resistor. The resistor is connected to the transistor between a first node and a second node. In a programming mode, the memory cell is programmed. The step of programming the memory cell includes providing a first controlling voltage to a gate of the transistor, providing a first setting voltage to the first node, and providing a second setting voltage to the second node. When it is determined that the memory cell has been successfully programmed, a specific action is executed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of Taiwan Patent Application No.098139877, filed on Nov. 24, 2009, the entirety of which is incorporatedby reference herein.

BACKGROUND OF THE DISCLOSURE

1. Technical Field

The disclosure relates to a control method, and more particularly to acontrol method for at least one memory cell.

2. Description of the Related Art

The impedance of a resistance type memory is easily differentiatedbetween a low state and a high state. Efficiency of the resistance typememory becomes lower as time goes by. Thus, for a resistance type memoryin operation for a long period of time, error may occur in reading orwriting thereof.

BRIEF SUMMARY OF THE DISCLOSURE

A control method for at least one memory cell is provided. The memorycell comprises a transistor and a resistor. The resistor is connected tothe transistor between a first node and a second node. An exemplaryembodiment of a control method for at least one memory cell is describedin the following. In a programming mode, the memory cell is programmed.The step of programming the memory cell comprises providing a firstcontrolling voltage to a gate of the transistor, providing a firstsetting voltage to the first node, and providing a second settingvoltage to the second node. It is determined whether the memory cell hasbeen successfully programmed. If the memory cell has been successfullyprogrammed, a specific action is executed.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by referring to thefollowing detailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1A is a schematic diagram of an exemplary embodiment of a controlmethod of the disclosure;

FIG. 1B is a schematic diagram of an exemplary embodiment of a memorycell of the disclosure;

FIG. 2 is a schematic diagram of an exemplary embodiment of a specificaction of the disclosure

FIGS. 3A, 3B, 4A, and 4B are schematic diagrams of other exemplaryembodiments of the specific action of the disclosure;

FIG. 5A is a timing diagram of an exemplary embodiment of the controlmethod of the disclosure;

FIG. 5B is a timing diagram of another exemplary embodiment of thecontrol method of the disclosure;

FIG. 6 is a schematic diagram of another exemplary embodiment of thecontrol method of the disclosure; and

FIG. 7 is a schematic diagram illustrating a result utilizing thecontrol method of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The following description is of the contemplated mode of carrying outthe disclosure. This description is made for the purpose of illustratingthe general principles of the disclosure and should not be taken in alimiting sense. The scope of the disclosure is determined by referenceto the appended claims.

FIG. 1A is a schematic diagram of an exemplary embodiment of a controlmethod of the disclosure. The control method is applied to at least onememory cell. FIG. 1B is a schematic diagram of an exemplary embodimentof a memory cell of the disclosure. The memory cell 100 comprises atransistor 111 and a resistor 113. The transistor is serially connectedto the resistor 113 between nodes 115 and 117. In this embodiment, whenthe memory cell 100 is programmed, the impedance of the memory cell 100is in a low state. When the memory cell 100 is reset, the impedance ofthe memory cell 100 is in a high state.

Referring FIG. 1A, the memory cell is programmed in a programming mode(step S120). In this embodiment, the step S120 comprises stepsS121˜S123. The disclosure does not limit the sequence of executing thesteps S121˜S123. In one embodiment, the steps S121˜S123 are sequentiallyexecuted. In another embodiment, the steps S121˜S123 are notsequentially executed.

A first controlling voltage Vg1 _((SET)) is provided to the gate of thetransistor 111 (step S121). A first setting voltage Vt1 _((SET)) isprovided to the node 115 (step S122). A second setting voltage Vt2_((SET)) is provided to the node 117 (step S123).

It is determined whether the memory cell 100 has been successfullyprogrammed (step S124). When the memory cell 100 has been successfullyprogrammed, the impedance of the memory cell 100 is in a low state.Thus, the state of the impedance of the memory cell 100 may be utilizedto determine whether the memory cell 100 has been successfullyprogrammed.

If the memory cell 100 has been successfully programmed (i.e. theimpedance of the memory cell 100 is in a low state), the programmingprocedure ends (step S125). If it is determined that the memory cell 100has not been successfully programmed (i.e. the impedance of the memorycell 100 is in a high state), a specific action is executed (step S126).

The disclosure does not limit the type of the specific action. A moredetailed description follows. FIG. 2 is a schematic diagram of anexemplary embodiment of a specific action of the disclosure. In thisembodiment, when the memory cell 100 has not been successfullyprogrammed, the specific action is to reset the memory cell 100. Whenthe memory cell 100 is reset, the impedance of the memory cell 100 is ina high state.

In this embodiment, the step 200 of resetting the memory cell 100comprises steps S211˜S213. In the step S211, a second controllingvoltage Vg2 _((RES)) is provided to the gate of the transistor 111. Inone embodiment, the controlling voltage Vg1 _((SET)) is less than thesecond controlling voltage Vg2 _((RES)).

In the step S212, a first reset voltage Vs1 _((RES)) is provided to thenode 115. In the step S213, a second reset voltage Vs2 _((RES)) isprovided to the node 117.

In one embodiment, the first setting voltage Vt1 _((SET)) and the secondreset voltage Vs2 _((RES)) are positive. In this case, the secondsetting voltage Vt2 _((SET)) is equal to the first reset voltage Vs1_((RES)). For example, the second setting voltage Vt2 _((SET)) and thefirst reset voltage Vs1 _((RES)) are ground voltages. In someembodiments, the first setting voltage Vt1 _((SET)) is greater than thesecond reset voltage Vs2 _((RES)), but the disclosure is not limitedthereto.

In another embodiment, the first setting voltage Vt1 _((SET)) ispositive and the first reset voltage Vs1 _((RES)) is negative. In thiscase, the second setting voltage Vt2 _((SET)) is equal to the secondreset voltage Vs2 _((RES)). For example, the second setting voltage Vt2_((SET)) and the second reset voltage Vs2 _((RES)) are ground voltages.

Further, the disclosure does not limit the sequence of the stepsS211˜S213. In this embodiment, the steps S211˜213 are sequentiallyexecuted. In other embodiments, the steps S211˜213 are not sequentiallyexecuted.

FIG. 3A is a schematic diagram of another exemplary embodiment of aspecific action of the disclosure. FIG. 3A is similar to FIG. 2 exceptfor the addition of steps S310 and S321˜S322. In this embodiment, thestep S310 is to program the memory cell 100 again.

The step S310 comprises steps S311˜S313. In the step S311, a thirdcontrolling voltage Vg3 _((SET)) is provided to the gate of thetransistor 111. In one embodiment, the third controlling voltage Vg3_((SET)) is less than the second controlling voltage Vg2 _((RES)). Inanother embodiment, the third controlling voltage Vg3 _((SET)) is equalto the first controlling voltage Vg1 _((SET)).

In the step S312, a third setting voltage Vt3 _((SET)) is provided tothe node 115. In one embodiment, the third setting voltage Vt3 _((SET))is greater than the first setting voltage Vt1 _((SET)).

In the step S313, a fourth setting voltage Vt4 _((SET)) is provided tothe node 117. In one embodiment, the fourth setting voltage Vt4 _((SET))is equal to the second setting voltage Vt2 _((SET)).

In some embodiments, the third controlling voltage Vg3 _((SET)) isgreater than the first controlling voltage Vg1 _((SET)). In this case,the third setting voltage Vt3 _((SET)) is equal to the first settingvoltage Vt1 _((SET)) and the fourth setting voltage Vt4 _((SET)) isequal to the second setting voltage Vt2 _((SET)). Additionally, thethird controlling voltage Vg3 _((SET)) is less than the secondcontrolling voltage Vg2 _((RES)), but the disclosure is not limitedthereto.

Furthermore, the disclosure does not limit the sequence of executing thesteps 200 and S310. In FIG. 3A, the step S200 of resetting the memorycell is executed and then the step S310 of programming the memory cellis executed again. In some embodiments, the step S310 of programming thememory cell is executed and then the step S200 of resetting the memorycell is executed as shown in FIG. 3B.

Similarly, the disclosure does not limit the sequence of the stepsS311˜S313. In one embodiment, the steps S311˜S313 are sequentiallyexecuted. In another embodiment, the steps S311˜S313 are notsequentially executed.

Referring to FIG. 3A, when the step S310 is executed, it is determinedwhether the memory cell has been successfully programmed (step S321). Ifthe memory cell has been successfully programmed, the programmingprocedure ends (step S322). If the memory cell has not been successfullyprogrammed, the step S200 is executed to reset the memory and againprogram the memory cell. At this time, the times of programming thememory cell is 3.

When the memory cell is reset again, the second controlling voltage Vg2_((RES)), the first reset voltage Vs1 _((RES)), the second reset voltageVs2 _((RES)) are maintained at levels which are the same as thatpreviously utilized, in one embodiment. In other words, the voltages forresetting the memory cell during a first attempt are equal to thevoltage for resetting the memory cell during a second attempt.

However, a portion of the voltages for programming the memory cellduring a third attempt may not be equal to a portion of the voltages forprogramming the memory cell during the second attempt. For example, whenthe memory cell has been programmed during a first attempt, the thirdcontrolling voltage Vg3 _((SET)) may be 1.4V, the third setting voltageVt3 _((SET)) may be 2.0V, and the fourth setting voltage Vt4 _((SET))may be 0V.

If it is determined that the memory cell has not been successfullyprogrammed following the first attempt, the third controlling voltageVg3 _((SET)) may be maintained at 1.4V or adjusted to 2.0V, the thirdsetting voltage Vt3 _((SET)) may be adjusted to 2.5V or maintained at2.0V, and the fourth setting voltage Vt4 _((SET)) may be maintained at0V to program the memory during a second attempt.

If it is determined that the memory cell has not been successfullyprogrammed during a second attempt, the third controlling voltage Vg3_((SET)) may be maintained at 1.4V or adjusted to 2.5V, the thirdsetting voltage Vt3 _((SET)) may adjusted to 3.0V or maintained at 2.0V,and the fourth setting voltage Vt4 _((SET)) may be maintained at 0V toprogram the memory during a third attempt.

In one embodiment, if it is determined that the memory cell has not beensuccessfully programmed, the voltage of the node 115 is increased tosuccessfully program the memory cell. In another embodiment, if it isdetermined that the memory cell has not been successfully programmed,the voltage of the node 115 is maintained and the controlling voltageprovided to the transistor 111 is increased such that the impedance ofthe memory cell 100 is adjusted to a low state.

FIG. 4A is a schematic diagram of another exemplary embodiment of aspecific action of the disclosure. FIG. 4A is similar to FIG. 3A exceptfor the addition of step S330. The step S330 is similar to the step S310except for the voltages, wherein the voltages utilized in the step S330are different from the voltage utilized in the step S310.

In the step S331, a fourth controlling voltage Vg4 _((SET)) is providedto the gate of the transistor 111. In one embodiment, the fourthcontrolling voltage Vg4 _((SET)) of the step S331 is equal to the thirdcontrolling voltage Vg3 _((SET)) of the step S310. The third controllingvoltage Vg3 _((SET)) may be equal to the first controlling voltage Vg1_((SET)) of step S121 shown in FIG. 1A. In this case, the fourthcontrolling voltage Vg4 _((SET)) is less than the second controllingvoltage Vg2 _((RES)) of the step S200.

In the step S332, a fifth setting voltage Vt5 _((SET)) is provided tothe node 115. In the step S333, a sixth setting voltage Vt6 _((SET)) isprovided to the node 117. In one embodiment, the fifth setting voltageVt5 _((SET)) is greater than the third setting voltage Vt3 _((SET)) ofthe step S310. Additionally, the third setting voltage Vt3 _((SET)) ofthe step S310 is greater than the first setting voltage Vt1 _((SET)) ofthe step S122 shown in FIG. 1A.

In above embodiments, the difference between the fifth setting voltageVt5 _((SET)) and the third setting voltage Vt3 _((SET)) is equal to thedifference between the third setting voltage Vt3 _((SET)) and the firstsetting voltage Vt1 _((SET)). In this case, the sixth setting voltageVt6 _((SET)) is equal to the fourth setting voltage Vt4 _((SET)) and thefourth setting voltage Vt4 _((SET)) is equal to the second settingvoltage Vt2 _((SET)).

In other embodiments, the fourth controlling voltage Vg4 _((SET)) of thestep S331 is greater than the third controlling voltage Vg3 _((SET)) ofthe step S310. The third controlling voltage Vg3 _((SET)) is greaterthan the first controlling voltage Vg1 _((SET)) of the step S121 shownin FIG. 1A. In this case, the fifth setting voltage Vt5 _((SET)) isequal to the third setting voltage Vt3 _((SET)) of the step S310. Thethird setting voltage Vt3 _((SET)) is equal to the first setting voltageVt1 _((SET)) of the step S122 shown in FIG. 1A.

Additionally, the sixth setting voltage Vt6 _((SET)) of the step S333 isequal to the fourth setting voltage Vt4 _((SET)) of the step S310. Thefourth setting voltage Vt4 _((SET)) is equal to the second settingvoltage Vt2 _((SET)) of the step S123 shown in FIG. 1A. In oneembodiment, the fourth controlling voltage Vg4 _((SET)) is less than thesecond controlling voltage Vg2 _((RES)) of the step S200.

FIG. 5A is a timing diagram of an exemplary embodiment of the controlmethod of the disclosure. During the programming period Tp1, settingvoltages are provided to a memory cell. During the read period Tr1, thestate of the memory cell is read. If the impedance of the memory cell isin a high state, a reset voltage Vs_((RES)) is provided to the memorycell to reset the memory cell during the reset period T_(RES1).

Then, new setting voltages are provided to the memory cell during theprogramming period Tp2, wherein a portion of the setting voltages duringthe programming period Tp2 is greater than the portion of the settingvoltages during the programming period Tp1. During the read period Tr2,the state of the memory cell is read again. If the impedance of thememory cell is in a high state, the memory cell is reset again duringthe reset period T_(RES2).

Next, new setting voltages are provided to the memory cell during theprogramming period Tp3, wherein a portion of the setting voltages duringthe programming period Tp3 is greater than the portion of the settingvoltages during the programming period Tp2. During the read period Tr3,the state of the memory cell is read again until the impedance of thememory cell is in a low state.

In this embodiment, a portion of the setting voltages Vt_((SET)) isgradually increased, but the disclosure is not limited thereto. In someembodiments, for the duration of the programming periods Tp1˜Tp3, thereset periods T_(RES1), T_(RES2) are adjusted or a portion of the resetvoltages Vs_((RES)) is gradually increased to successfully program thememory cell.

FIG. 5B is a timing diagram of another exemplary embodiment of thecontrol method of the disclosure. During the programming period Tp4,setting voltages are provided to the memory cell. During the resetperiod, the state of the memory cell is read. If the impedance of thememory cell is in a high state, new setting voltages are provided to thememory cell during the programming period Tp5, wherein a portion of thesetting voltages during the programming period Tp5 is greater than aportion of the setting voltages during the programming period Tp4.

During the reset period T_(RES3), reset voltages are provided to thememory cell. During the programming period Tp6, new setting voltages areprovided to the memory cell. In this embodiment, the setting voltagesduring the programming period Tp6 are the same as the setting voltagesduring the programming period Tp4. During the read period Tr5, the stateof the memory cell is read. If the impedance of the memory cell is in ahigh state, new setting voltages are provided to the memory cell duringthe programming period Tp7, wherein a portion of the setting voltagesduring the programming period Tp7 is greater than a portion of thesetting voltages during the programming period Tp6. In this embodiment,the setting voltages during the programming period Tp4 are the same asthe setting voltages during the programming period Tp6.

FIG. 6 is a schematic diagram of another exemplary embodiment of thecontrol method of the disclosure. FIG. 6 is similar to FIG. 1A exceptfor the addition of step S610. The step S610 comprises steps S611˜S613.

In a forming mode, an initial voltage Vg_((INI)) is provided to the gateof the transistor 111 (step S611). In one embodiment, the initialvoltage Vg_((INI)) is less than the first controlling voltage Vg1_((SET)) of the step S121 shown in FIG. 1A, but the disclosure is notlimited thereto. In some embodiments, the initial voltage Vg_((INI)) isless than the second controlling voltage Vg2 _((RES)) of the step S211shown in FIG. 2.

In the step S612, a first initial setting voltage V_(SI1) is provided tothe node 115. In one embodiment, the first initial setting voltageV_(SI1) is greater than the first setting voltage Vt1 _((SET)) of thestep S122 shown in FIG. 1A. In other embodiments, the first initialsetting voltage V_(SI1) is greater than the fifth setting voltage Vt5_((SET)) of the step S332 shown in FIG. 4A.

In the step S613, a second initial setting voltage V_(SI2) is providedto the node 117. In one embodiment, the second initial setting voltageV_(SI2) is equal to the second setting voltage Vt2 _((SET)) of the stepS123 shown in FIG. 1A.

When the memory cell has been successfully programmed, the impedance ofthe memory cell is in a low state. If the impedance of the memory cellis in a high state, it means that the memory cell has not beensuccessfully programmed. Thus, a specific action is executed.

The specific action is to reset the memory cell or program the memorycell again. In one embodiment, the specific action is to reset thememory cell and then program the memory cell again. In anotherembodiment, the specific action is to again program the memory cell andthen reset the memory cell. When the memory cell is programmed again,high voltages are provided to the transistor to successfully program thememory cell.

FIG. 7 is a schematic diagram illustrating a result utilizing thecontrol method of the disclosure. Assuming the control method is appliedto one thousand memory cells. After programming the memory cells, theimpedances of all memory cells are in a low state (below 10Ω).

While the disclosure has been described by way of example and in termsof the embodiments, it is to be understood that the disclosure is notlimited to the disclosed embodiments. To the contrary, it is intended tocover various modifications and similar arrangements (as would beapparent to those skilled in the art). Therefore, the scope of theappended claims should be accorded the broadest interpretation so as toencompass all such modifications and similar arrangements.

1. A control method for at least one memory cell comprising a transistorand a resistor connected to the transistor in series between a firstnode and a second node, comprising: programming the memory cell in aprogramming mode, wherein the step of programming the memory cellcomprises: providing a first controlling voltage to a gate of thetransistor; providing a first setting voltage to the first node; andproviding a second setting voltage to the second node; determiningwhether the memory cell has been successfully programmed; when thememory cell has been successfully programmed, impedance of the memorycell is in a first state, and when the memory cell has not beensuccessfully programmed, a specific action is executed, wherein thespecific action is to reset the memory cell, and the step of resettingthe memory cell comprises: providing a second controlling voltage to thegate of the transistor, wherein the first controlling voltage is lessthan the second controlling voltage; providing a first reset voltage tothe first node; and providing a second reset voltage to the second node,wherein the impedance of the memory cell is in a second state after thestep of resetting the memory cell, and wherein the impedance of thememory cell in the second state is higher than the impedance of thememory cell in the first state.
 2. The control method as claimed inclaim 1, wherein the first setting voltage and the second reset voltageare positive.
 3. The control method as claimed in claim 2, wherein thesecond setting voltage is equal to the first reset voltage.
 4. Thecontrol method as claimed in claim 1, wherein the first setting voltageis positive and the first reset voltage is negative.
 5. The controlmethod as claimed in claim 4, wherein the second setting voltage isequal to the second reset voltage.
 6. The control method as claimed inclaim 1, wherein the specific action further comprises programming thememory cell again, wherein the step of programming the memory cell againcomprises: providing a third controlling voltage to the gate of thetransistor; providing a third setting voltage to the first node; andproviding a fourth setting voltage to the second node.
 7. The controlmethod as claimed in claim 6, wherein the third controlling voltage isequal to the first controlling voltage and the third controlling voltageis less than the second controlling voltage.
 8. The control method asclaimed in claim 7, wherein the third setting voltage is greater thanthe first setting voltage.
 9. The control method as claimed in claim 8,wherein the fourth setting voltage is equal to the second settingvoltage.
 10. The control method as claimed in claim 6, wherein the thirdcontrolling voltage is greater than the first controlling voltage andthe third controlling voltage is less than the second controllingvoltage.
 11. The control method as claimed in claim 10, wherein thethird setting voltage is equal to the first setting voltage and thefourth setting voltage is equal to the second setting voltage.
 12. Thecontrol method as claimed in claim 6, wherein the specific action is toexecute the step of resetting the memory cell and then execute the stepof programming the memory cell again.
 13. The control method as claimedin claim 6, wherein the specific action is to execute the step ofprogramming the memory cell again and then execute the step of resettingthe memory cell.
 14. The control method as claimed in claim 6, whereinthe step of programming the memory cell again further comprises:providing a fourth controlling voltage to the gate of the transistor;providing a fifth setting voltage to the first node; and providing asixth setting voltage to the second node.
 15. The control method asclaimed in claim 14, wherein the first, the third, and the fourthcontrolling voltages are the same and the fourth controlling voltage isless than the second controlling voltage.
 16. The control method asclaimed in claim 15, wherein the fifth setting voltage is greater thanthe third setting voltage and the third setting voltage is greater thanthe first setting voltage.
 17. The control method as claimed in claim16, wherein the difference between the third and the fifth settingvoltages is equal to the difference between the first and the thirdsetting voltages.
 18. The control method as claimed in claim 17, whereinthe sixth setting voltage is equal to the fourth setting voltage and thefourth setting voltage is equal to the second setting voltage.
 19. Thecontrol method as claimed in claim 14, wherein the fourth controllingvoltage is greater than the third controlling voltage, the thirdcontrolling voltage is greater than the first controlling voltage, andthe fourth controlling voltage is less than the second controllingvoltage.
 20. The control method as claimed in claim 19, wherein thefifth setting voltage is equal to the third setting voltage, the thirdsetting voltage is equal to the first setting voltage, the sixth settingvoltage is equal to the fourth setting voltage, and the fourth settingvoltage is equal to the second setting voltage.
 21. The control methodas claimed in claim 14, wherein the specific action is to execute thestep of resetting the memory cell and then execute the step ofprogramming the memory cell again.
 22. The control method as claimed inclaim 14, wherein the specific action is to execute the step ofprogramming the memory cell again and then execute the step of resettingthe memory cell.
 23. The control method as claimed in claim 14, furthercomprising a forming mode, wherein in the forming mode: providing aninitial voltage to the gate of the transistor; providing a first initialsetting voltage to the first node, wherein the first initial settingvoltage is greater than the fifth setting voltage; and providing asecond initial setting voltage to the second node.
 24. The controlmethod as claimed in claim 1, further comprising a forming mode, whereinin the forming mode: providing an initial voltage to the gate of thetransistor; providing a first initial setting voltage to the first node;and providing a second initial setting voltage to the second node. 25.The control method as claimed in claim 24, wherein the initial voltageis less than the first controlling voltage.
 26. The control method asclaimed in claim 25, wherein the first initial setting voltage isgreater than the first setting voltage.
 27. The control method asclaimed in claim 26, wherein the second initial setting voltage isequals to the second setting voltage.
 28. The control method as claimedin claim 24, wherein the second controlling voltage is greater than theinitial voltage.